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QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi

Barbara Jager·Stefan Kretzer·Marco Stratmann·Werner Vogelsang
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Abstract

Recent preliminary PHENIX data are consistent with a negative and sizable longitudinal double-spin asymmetry A_LL^pi for pi^0 production at moderate transverse momentum p_perp \simeq 1 - 4 GeV and central rapidity. By means of a systematic investigation of the relevant degrees of freedom we show that the perturbative QCD framework at leading power in p_perp produces at best a very small negative asymmetry in this kinematic range.

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Barbara Jager, Stefan Kretzer, Marco Stratmann, Werner Vogelsang. 2004-05-19. QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi. https://doi.org/10.1103/physrevlett.92.121803

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